resumed at a later time. Ryu's movements are directed using the console gamepad. The game's control system, which comprises the left thumbstick, two attack buttons, and a block button, was described as fluid and responsive, and Ninja Gaiden was regarded as having one of the deeper combat engines among Xbox games at the time, comparing well to the action-adventures God of War and Devil May Cry. Eric Williams, the designer of the God of War combat engine, explained that Ninja Gaiden prohibits players from stopping or changing attacks in mid-stroke. In contrast, God of War allows players to do so, and Devil May Cry grants this freedom to certain attacks. Williams said that, compared to those two games, the combat system in Ninja Gaiden was harder to master; however, it lets players fight their computer controlled foes on equal terms. Ninja Gaiden features a large selection of weapons for Ryu to wield, each with advantages and disadvantages that affect the way the player approaches combat. These include one-handed swords, such as the Dragon Sword and Kitetsu, which grant quick attacks, and a move called the "Flying Swallow", which allows Ryu to leap and slash through enemies. In addition these light weapons allow Ryu to smash foes into the ground and perform his signature Izuna Drop—a spinning piledriver. Heavy weapons, such as the Dabilahro and the Unlabored Flawlessness, are slow but cause more damage to opponents. With flails and staves, the player can string together long sequences of attacks. To engage distant foes Ryu can throw shuriken and shoot arrows. In addition to using standard melee techniques, Ryu can employ essences—colored globes of energy that are released on the death of enemies and absorbed into Ryu's body when he comes into proximity with them. Essences have an important role in general gameplay, acting to heal Ryu, restore his magic, or increase his cash. However, in combat the player can cause Ryu to deliberately draw in essences, which can then be used to unleash powerful attacks known as Ultimate Techniques that allow Ryu to damage enemies without taking damage himself. These techniques deal heavy damage and make Ryu immune to injury for a short time. Ninja Gaiden also provides Ryu with magical spells in the form of ninpo spells. When activated by the player, these make Ryu cast fireballs, ice storms, or bolts of lightning. Functioning in a similar manner to the